> It looks like in the ecosystem check a bunch of violations were removed with no fix, so I'm wondering if a syntax error was introduced by the fix. Maybe when there is a default argument something goes wrong?

I think this happens for projects where the ruff.toml or pyproject.toml contains fix = true. I also got tripped up by this behavior in some of my pull requests. I think it would be a good idea to change the ecosystem script to pass --no-fix, so this doesn't happen, since the output will always be interpreted incorrectly when fixes have been applied (this can also lead to other confusing things like new E501 flags, because the fix caused a line to get too long, or an unrelated unfixable violation getting flagged, because the fix caused the violation to be slightly offset, so you see a +1 -1 for that violation).

Originally posted by @Daverball in #15139 (comment)